The present invention concerns an energy converter for feeding an autonomous apparatus with low consumption from thermocouples with a low temperature difference constituting a source of very low voltage and low but not nil internal resistance, the realization of the thermocouples, as well as an industrial manufacture process of the thermocouples.
Many apparatuses have to function autonomously, that is to say that they comprise their own power supply. It is the case of portable apparatuses such as watches or auricular amplifiers which can not be permanently connected to an electrical feeding system. It is also the case of apparatuses placed in difficulty accessible places, such as intrusion detectors used in alarm systems; they are placed for example in openings such as windows where it is difficult and expensive to bring a feeding cable.
These autonomous apparatuses with low consumption are currently fed by cells or rechargeable elements whose life or discharge duration is limited, what involves relatively frequent replacement or refill operations and obliges to store piles or accumulators of replacement for avoiding an interruption of the functioning. One has already envisaged to exploit sources of very low voltage by using converters providing an output voltage in the order of some volts for feeding apparatuses with low consumption reduced without interruption of functioning by using a self oscillating circuit comprising a step-up transformer and a field effect transistor whose drain-source path is connected in the primary of the transformer.
These known converters are conceived for oscillating in such a way to increase the voltage and they have a mediocre efficiency which does not allow to extract, from sources of very low voltage, the necessary power for the functioning of a watch or an auditive apparatus. Furthermore, the functioning of these oscillators is strongly disturbed when the load becomes significant; they can stop oscillating or even not start.
We know well documents: 1 (PETER WILSON xe2x80x9cV Switching Mode Power Suppliesxe2x80x9d), 2 (DE 14 37 235 A Philips), 3 (U.S. Pat. No. 3 679 918 A KEIZI), 4 (F. BUTLER xe2x80x9cTransistor Inverter Frequency Stabilized Circuit Suitable for Running a Tape Recorderxe2x80x9d, 5 (Patent Abstracts of JAPAN vol 5, nxc2x078 (E-058)), 7 (FR 1 162 168 A Soci{acute over (ete gene)}rale d""xc3xa9quipement pour l""automobile, la locomotion aerienne).
All these documents comprise oscillator circuits, the diagrams described in documents 3 and 7 are the closest to the invention, however none of them is able to spontaneously oscillate when the circuit is fed by a direct voltage as low as 10 to 200 millivolts. This is due to the threshold effect occurring in the base-emitter junction of the oscillator transistor (in the order of 0.5 volt). A bipolar transistor has to be polarized for being able to be used in a self oscillating circuit. This is not the case of the JFET transistor used in the present invention, it has a variable resistance when the gate-source voltage Vgs fluctuates around zero volt. The document 1 as well as the document 6 (U.S. Pat. No. 3,913,000 A GILBERT, CARDWELL) show converter circuits using the load of an inductance for converting a voltage, the process is well known as stated in the document 6, FIG. 1. What is new in the framework of the present invention is the association of the self-oscillating circuit and of the chopping converter which is optimized for the very low powers (10 microwatts to 10 milliwatts), without other source of energy for the operation of the converter.
The basic problem solved by the invention is to provide an energy converting circuit having an efficiency allowing one to extract the desired power and voltage from sources of electrical power of very low voltage and whose functioning is insured even for a significant load. For this purpose, the object of the invention is an energy converting circuit which boosts the voltage provided by a source at low direct voltage with small internal resistance, comprising a self-oscillating circuit, functioning at a very low voltage, using a voltage step-up transformer generating the control signals of two chopper-step-up transformers with alternate operation, of the type comprising an enhancement mode field effect transistor which is used as a synchronous switch with the self-oscillating circuit, which is connected in series with an inductance to the terminals of said source and which is connected to the user circuit through a diode.
The use of chopper-step-up circuits allows to extract approximately 50% of the available power in the source. One can feed apparatuses with a voltage of some volts from a source whose voltage is in the order of some tens of millivolts.
Moreover, the functioning is insured for important loads.
Advantageously, a voltage limiting diode and a condenser of great capacity or an accumulator is connected to the output terminals.
In this manner, the output voltage is determined to the desired value.
The invention has also for object a reversible converter circuit, characterized in that it comprises two converter circuits which are antiparallel connected to the source and bound to the output terminals through four switches which are controlled two by two by two supplementary windings of the transformer of the operating converter and in that each converter comprises a blocking device blocking the other converter when it is operating.
Such circuit allows to extract energy provided by a source whose polarity is variable. The two converters operate alternatively according to the polarity of the source, the operating converter blocking the other converter for avoiding any power loss in the non operating converter.
Advantageously, the blocking device comprises a third supplementary winding of the transformer to whose terminals is connected a rectifier circuit generating a direct voltage blocking the self-oscillating circuit of the non operating converter.
The invention had also for object a device for feeding an autonomous portable apparatus from a thermal system comprising a hot source and a cold source with a low temperature difference between them, such as the epidermis of a human being and the ambient atmosphere, characterized in that it is constituted by a converter circuit in which the electrical source is constituted by an assembly of Seebeck effect detectors connected between the two thermal sources. This converter is also suitable for extracting the power of photovoltaic source.
Such a feeding device can be integrated in a watch or an auditive apparatus. It can also be used for recharging a rechargeable element.